Depends on what you mean. Inbound email is checked for authentication (SPF, DKIM, DMARC, etc) as part of the spam filter. For outbound email, we ask you to set

Depends on what you mean. Inbound email is checked for authentication (SPF, DKIM, DMARC, etc) as part of the spam filter. For outbound email, we ask you to set up at least one of SPF or DKIM before you can send.